The U.S. patent of Garland et al., U.S. Pat. No. 5,211,125, issued May 18, 1993, relates to an apparatus and a method for performing external surface work on generally vertical sidewall areas of a ship hull. Typical of the work to be conducted is blast-cleaning, and painting of those areas of a ship hull. Various elaborations and modifications to the apparatus and method are disclosed in the U.S. patent application of Goldbach et al., Ser. No. 08/027,802, filed Mar. 3, 1993, now U.S. Pat. No. 5,398,632, and in the U.S. patent application of Goldbach et al. Ser. No. 08/099,434, filed Jul. 30, 1993 now U.S. Pat. No. 5,353,729.
In general, the above-identified U.S. patent and applications disclose placing towers along at least a portion of the sidewall of a ship (while the ship is in drydock or afloat), and enshrouding the tower or towers against the hull, to create an enclosed spaced, which is ventilated by means of an air-processing system. The air-processing system heats and conditions the air being supplied to the enclosed space, and extracts dust and volatile organic chemicals from the air exhausted from the enclosed space.
Work on the hull is accomplished within the enclosed space, from a platform mounted to a vertically elevatable trolley supported on a respective tower. During cleaning operations, the output of a blast cleaning device is applied from the platform against a respective increment of the ship hull. During painting operations, a paint spraying device is applied from the platform against a respective increment of the ship hull.
Although much of the sidewall of a ship hull is substantially vertical, compound curvature is exhibited in bow and stern areas, and even amidship the exterior surface curves under at the sidewall base, from vertical to horizontal. Much of the exterior surface of the bottom of a ship hull is generally or substantially horizontal (particularly if the ship is in the economically significant class of bulk cargo vessels, such as very large crude carriers).
The above-identified U.S. patent and applications disclose, among them, a way of applying surface work in the curved bow, stern and sidewall base (or bilge) areas of the ship hull sidewall. An important part of this way of accommodating carrying out the process to the fact of curvature in those areas, is that the work platform is mounted to the trolley by a set of arms which are extensible and retractable towards and away from the trolley so that where the hull curves away from the respective tower, the arms can be extended (differentially relative to one another, if need be), for always maintaining uniformity in the spacing of the work platform from the particular increment of ship hull sidewall being worked on, regardless of whether that increment is part of a large substantially vertical area, or is part of a transitional area where the hull is curving away from the tower.
The shrouding for the tower or towers includes not only portions which extend around the rear and sides of the tower or set of side-by-side towers, and over the top, but also portions which seal with the support surface on which the tower or towers are supported (e.g., a drydock deck if the ship is in drydock, or an alongside barge if the ship is afloat while being worked on). Further, at the left and right ends of the enclosure, the shrouding extends forward to seal against the ship hull sidewall surface, e.g., with the aid of a batwing-like skeletal framework for flexible plastic fabric sheeting having magnetic grippers secured along its leading edge. At the base of the sidewall, at the limit where the hull exterior surface curves away too radically towards horizontality to be able to be effectively worked on using the above-described tower based apparatus (or near the waterline, in the case of a ship afloat), the prior art system referred to above provides the shrouding with a bib-like lower frontal curtain element which defines the lower frontal part of the confined space of the tower or set of towers. The upper edge of the curtain is similarly attached and sealed to the hull, and the lower or rear edge is sealed to the tower support surface, left and right edges are integrated into the left and right end curtains for the shrouding.
Accordingly, paint chips, metal flakes, spent abrasive, paint overspray and the like can be kept from falling into, or being washed by rain into the water in the vicinity of the work being done on the ship hull.
The above-identified U.S. patent and patent applications further disclose, among them, ways and means for recovering spent abrasive, separating it from paint chips and other debris as well as from used-up spent abrasive (i.e., which has become too size-reduced and/or rounded in particle shape), and recycling the portion of it which is reuseable, together with make-up unused abrasive grit, to the abrasive blasting applicator devices.
Abrasive blasting applicator devices which are closed-cycle are known in the art, and are referred to and further identified in the above-identified U.S. patent and patent applications. In such a device, the output nozzle or equivalent structure of the device is surrounded around the rear and sides, by a forwardly extending structure, the effective forward edge of which forms a trap against the surface being blast cleaned, so that much of the spent abrasive, paint chips, scale and the like which rebound from or are blasted free of the work surface, rather than falling to the deck or other undersurface, are caught within the trap, and either funnelled to a collector for separation and recycling back to the blast applicator device, or for a plurality of cycles, may simply be recycled, without substantial separation, within the device, until the grit has become too size-reduced and too adulterated with paint chips and scale, whereupon, the contained supply of grit of the particular blaster is wholly or partly replaced with fresh abrasive grit.
The above-identified U.S. patent and applications further disclose, among them, that whereas in some instances, the work-applying device such as an abrasive blaster or a paint sprayer, can be a hand-held unit being supported and manipulated by a human operator standing on the elevatable platform of a respective shrouded tower, in other instances, the work applicator is mounted on a carriage that is movable along rails extending in a left-to-right direction on the front and/or bottom of the elevatable platform. Indexing of the carriage along the platform can be under automated control, off-platform (remote) manual control and/or on-platform manual control (e.g., by a human operator operating the controls of a control panel).
Cleaning and painting of ship hulls and the like, using apparatus such as that described above as practiced by MMC Compliance Engineering, Inc. of Norfolk, Va., U.S.A., and the apparatus used, are called a CAPE.TM. system, by that company.
Although some of the same principles would be understood by a person of ordinary skill in the art, no doubt to be applicable to cleaning the generally or substantially horizontal, downwardly facing external surface of a ship hull in drydock, or similar structure, the above-identified U.S. patent and applications do not focus on cleaning such areas, or particularly show or describe ways and means for working on such surfaces.
Working on such a surface, particularly for blast cleaning it, presents unique handling problems associated with the weight of a preferred rotating wheel-type closed cycle abrasive blasting grit applicator, leakage of abrasive rebounding from the work, supporting and moving the applicator along successive swaths of the underside of the bottom of the hull.